47th Annual AAPG-SPE Eastern Section Joint Meeting

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Central Kentucky Reservoirs Associated With the Cincinnati Arch Affected by Structure and Tectonics


Central Kentucky structurally lies on the axis of the Cincinnati Arch, a major structural feature that separates the Appalachian Basin to the east from the Illinois Basin to the west. Structural features associated with the Cincinnati arch are the Jessamine dome to the north and the Nashville dome to the south. A structurally low feature, the Cumberland saddle, separates the two domes. Sedimentary evidence suggests that basement faulting and uplift of the Cincinnati Arch occurred as early as the Cambrian and was reactivated several times during various periods in geologic time. An unconformity occurs at the top of the Cambrian-Ordovician rocks resulting in extensive karst topography including residual hills and sink holes. The southern area along the arch has been extensively and successfully explored for hydrocarbons which are entrapped along an unconformity at the top of the Cambrian-Ordovician rocks. As a result of repeated uplift and shifting of the axis of the arch, numerous fractures occurred in the carbonates, both beneath and overlying the unconformity. Several extensive fault systems are present in the area, and many of them produce hydrocarbons on the upthrown side. The hydrocarbons were driven by fluids and gases and migrated along the eroded Cambrian-Ordovician surface laterally and upward onto topographic highs. Hydrocarbons generated from Devonian black shales migrated both vertically and horizontally from deep in the Appalachian and Illinois Basins through faults, fractures, joints, weakened bedding planes, vugs, breccias, unconformable surfaces, and along the flanks of the arch to accumulate in Cambrian, Ordovician, and Silurian reservoirs. Brecciated and fractured zones associated with the unconformity also serve as a host for hydrocarbons and sulfide mineralization containing varying amounts of galena, sphalerite, barite, calcite, and fluorite. The porosity characteristics of the carbonates are secondary, caused by chemical and physical changes such as dolomitization, hydrothermal activity, solution channels, or fractures. Compaction and cementation also affect porosity. The porosity, permeability, and pore-space distribution observed in core samples are related to the depositional environment, changes that have occurred after deposition, and tectonic activity.